1. Field of the Invention
The present invention relates to a method for coating a substrate with a selected material. More particularly, the present invention relates to a method for forming such coatings by using phase shifting of a dense phase gas.
2. Description of Related Art
In the manufacture of various articles or structures, it is often desirable to provide a coating on the finished structure in order to provide improved properties or performance. For example, a coating may be applied to a structure to provide a protective outer layer or to impart color to the structure. Known methods for forming such coatings include vapor deposition processes in which vapor phase materials are reacted in the presence of the substrate to form a solid material which deposits on the substrate. In another known process, a solution of the coating material in a solvent is applied to the surface of the substrate and then the solvent is evaporated, to leave the desired coating on the substrate. In some cases, the coating material is impregnated into the substrate, as in a static pressure impregnation process, in which pressure is applied directly to the coating material to force or propel it into the substrate. The pressure vehicle, which may be gas, hydraulic, or piston, contacts the coating material but does not function as a carrier or solvent for the material. While these processes have been widely used, each has limited material applications and capabilities. For example, vapor deposition methods are often used to deposit metallic coatings on external material surfaces. Solvent evaporation processes require the use of solvents which may have undesirable environmental impact. Static pressure impregnation processes put gross amounts of additive materials into or on to a substrate.
Consequently, there is a present need to provide a coating process which has a wider range of applications and which does not require the use of undesirable solvents which may damage the environment.